A typical Power over Ethernet (PoE) power communications system includes power-sourcing communications equipment (PSE) and a set of remotely-powered network devices (e.g., PDs or Powered Devices) that connect to the power-sourcing communications equipment through network cables. Power-sourcing communications equipment can include i) power supply circuitry to provide power through a cable to a respective network device and ii) transmit/receive circuitry to support data communications with a respective network device at the other end of a cable. Accordingly, when supplied power through the cable, a user of the respective network device is not burdened with having to separately connect his network devices to another power source such as a 115 volt wall outlet. Instead, the network device coupled to a port of the power-sourcing communications equipment relies on power received through the cable.
There are industry standards which attempt to provide guidelines for manufacturing certain types of power-sourcing communications equipment. For example, the IEEE 802.3af standard, which is also called the “Power over Ethernet” standard, defines ways to build Ethernet power-sourcing equipment and powered devices. In particular, the IEEE 802.3af standard identifies ways to deliver certain electrical features (e.g., 48 volts) of DC power over unshielded twisted-pair wiring (e.g., Category 3, 5, 5e or 6 network cables, patch cables, patch-panels, outlets and connecting hardware) to a variety of Ethernet devices such as IP phones, wireless LAN access points, laptop computers, web cameras, etc.
In the context of the IEEE 802.3 Ethernet Standard, which does not cover UPS applications and is limited to PSE and PD interactions, the power-sourcing communications equipment discussed above is referred to a Power Sourcing Equipment (PSE) and network devices coupling to the PSE (e.g., a switch device) through cables are known as Powered Devices (PDs).
According to one conventional technique, a PSE receives power from a power source such as an Uninterruptible Power Supply (UPS) that produces power based on primary power and, when needed, backup power. When the primary power (e.g., 115 or 230 volts or a DC voltage) fails due to a power outage, the power source relies on the backup power (e.g., power from capacitors, batteries, generator, etc.) to provide continued and uninterrupted power to the PSE. Preferably, the power source can transition to a use of the backup power so quickly that there is no interruption of power provided from the power source to the PSE. Consequently, the PSE can provide continuous power through cables to the associated PDs even during a power outage. Accordingly, some VOIP phone systems, wireless PD devices (such as 802.11 base stations) and other PDs include a central switch configured to provide power through cables to the end devices (e.g., PDs such as VOIP phones, 802.11 base stations etc.) thus alleviating the need for PDs that require power under all circumstances (uninterrupted power) to have separate individual power supplies.